Continuous positive airway pressure (CPAP) breathing increases alveolar and intrathoracic pressures, hampering venous return and pulmonary capillary flow. Bilevel positive airway pressure (BiPAP) breathing assuring lower expiratory pressure should impede less the pulmonary circulation. We aimed to compare the effects of CPAP and BiPAP breathing on pulmonary haemodynamics in patients with obstructive sleep apnoea (OSA). Nine male OSA patients (mean (+/- SD) apnoea-hypopnoea index (AHD = 46 +/- 22) were studied. In each patient, intravascular and oesophageal pressures were measured and mean transmural pulmonary artery and transmural wedge pressures were calculated. After baseline recordings, patients were submitted to 25 min of CPAP and BiPAP breathing delivered in random order. The pressure of 10 cmH2O for CPAP and 10/4 cmH2O for BiPAP was used. At baseline, subjects presented with normal pulmonary arterial pressures and cardiac output (Q'). CPAP breathing resulted in a slow increase in mean pulmonary intravascular pressure from 13.8 +/- 2.0 mmHg reaching 14.8 +/- 1.8 mmHg at the 25th minute of investigation (p < 0.05). Transmural pressure did not change. There was also no change in the Q' and in the pulmonary vascular resistance. BiPAP breathing had no effect on intravascular and transmural pressures, Q' and pulmonary vascular resistance. We conclude that continuous positive airway pressure breathing increases pulmonary intravascular but not transmural, true, pressure. Bilevel positive airway pressure breathing does not affect central pulmonary haemodynamics.

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